The invention relates to allocating data transmission resources in packet-switched data transmission and especially to optimizing radio interface resources in wireless packet-switched data transmission.
Third-generation mobile systems, called UMTS (Universal Mobile Telecommunication System) and IMT-2000 (International Mobile Telephone System), will provide not only circuit-switched speech services, but also packet-switched services for instance in the manner of the packet radio network GPRS (General Packet Radio Service) designed for the GSM system. Packet-switched data transmission enables the use of different data services by means of a mobile station and, on the other hand, the allocation of the resources of a mobile system, especially the radio interface, for each user as necessary.
When the user of a terminal in a UMTS system wants to use a packet-switched application, for instance to download a video file from the network to the terminal, the radio resource management system RRM of the UMTS system allocates to a radio bearer an application-based capacity reservation which not only depends on the used application but also on the available radio bearer parameters. In typical one-way data transmission, for instance when downloading a file from the network, a data rate of x bit/s can then be allocated to a terminal in the downlink direction (from the base station to the terminal) and a data rate of 0 bit/s in the uplink direction (from the terminal to the base station). In such an application, the uplink data transmission is typically not needed and consequently, there is no need to allocate resources to it.
One of the parameters defining the radio bearer is the method used by the terminal for compressing the header fields of data packets. Header compression of data packets being transmitted and decompression of data packets being received is performed on the packet data convergence protocol layer PDCP of the UMTS system. The PDCP layer of a terminal typically supports several header compression methods so as to enable connection set-up with as many network layer protocol types as possible. Some header compression methods may also need a reverse connection for making different acknowledgments and solving error situations. A certain bandwidth then needs also to be reserved for the reverse connection, but, on the other hand, the compression of the header field decreases the need for a bandwidth for a forward connection.
A problem with the above arrangement arises from using an application-based capacity allocation together with a header compression method which requires a bi-directional connection. If the terminal only has header compression methods requiring a bi-directional connection available to it and the terminal sends a capacity allocation request to an application which is typically uni-directional, such as the downloading of a file from the network described above, the radio resources management system RRM only allocates a one-way connection for the radio bearer on the basis of the application. The available compression methods do not then function and the connection cannot be set up without being able to reserve an adequate bandwidth also for the reverse connection using special arrangements comprising new capacity allocation requests. This is not possible in all situations and, in any case, such an arrangement complicates an optimal allocation of radio resources.